To most Americans, diseases with names like dengue fever, chikungunya, malaria, Chagas and leishmaniasis might sound like something out of a Victorian explorer’s tales of hacking through African jungles. Yet ongoing epidemics of these diseases are killing millions of people around the world. Now, disease experts are increasingly concerned these and other infections may become as familiar in the United States as West Nile or Lyme disease.

Few believe Americans face a killer epidemic from tropical diseases. But scientists who specialize in emerging infectious diseases say such illnesses may become more common here as the economic downturn batters an already weakened public health system, creating environmental conditions conducive to infectious diseases spread by insects or other animals. At the same time, such vector-borne diseases are capable of spreading around the world much more rapidly due to massive south-to-north immigration, rapid transportation, and global trade.

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Budget cuts over a period of years have left public health at all levels of government underfunded by $20 billion, according to a report published in the U.S. in October by the non-partisan Trust for America’s Health.

The recession has only piled on the pain, with states and counties being especially hard hit. For example, Washington’s King County was forced to cut roughly $19 million out of public health in its 2009 budget.

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A significant amount of the CDC funding for emerging diseases goes to salaries and state and local health departments, explained Dr. Ali Kahn, deputy director of the National Center for Zoonotic, Vector-Borne and Enteric Diseases at the CDC, “There is no doubt we could do a lot more in the U.S. and worldwide with additional funds,” said Kahn.

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Once ‘conquered,’ now returning

Diseases such as Chagas and leishmaniasis affect more than 13 million people around the world each year, according to experts. These vulnerabilities in America’s disease defensive shield comes at a time when worldwide changes have boosted the ability of such diseases to spread. Cities in tropical Asia and Africa, for example, “have gone from 4 million to 15 million people,” Gubler explained. “These are mega cities that have inadequate housing, water and sewer treatment, waste management,” Gubler said. “This creates ideal conditions for transmission of all kinds of infectious diseases.”

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American health officials thought they had conquered most such diseases after World War II through a combination of mosquito-killing campaigns and public health measures like draining swamps, improved housing, better sewage and waste control. As a result, medical professionals turned their attention to conditions like cancer and diabetes.

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In a June 2008 article in the journal PLOS Neglected Tropical Diseases, Dr. Peter Hotez, chairman of the department of microbiology, immunology and tropical medicine at George Washington University in Washington, D.C. wrote that Americans living in poverty, immigrants and those living in medically underserved regions suffer from a host of such diseases, including Chagas, dengue and leishmaniasis.

Increasingly, these diseases pose a risk to the rest of the country. For example, in 2007, in the middle of a drought that should have prevented large-scale mosquito breeding, Kern County, Calif. became the national epicenter of West Nile disease, which emerged in Africa and is spread by mosquitoes.

At least 140 confirmed cases, and four deaths, were recorded. At first, public health officials were mystified. They soon realized that because the county was an early victim in the national housing collapse, foreclosed and abandoned homes sat with partially filled swimming pools and spas serving as mosquito love motels.

Ten years ago, managers of hunting dog kennels in upstate New York began to notice that some of the foxhounds had contracted a mysterious illness.

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When experts from the CDC and Walter Reed Army Medical Center in Washington, D.C. finally identified the illness, they realized foxhounds in New York were dying of visceral leishmaniasis, a parasitic disease usually found in places like Brazil, the Middle East and India. The disease is transmitted by a type of sand fly.

Investigators still aren’t sure how the foxhounds caught the disease. At the time when Ostfeld and a group of interns set traps on the institute’s 2000 acres, they found sand flies all over the place.

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Diseases knocking on America’s door

What worries officials most is not that somebody could step off an airplane with a disease, but that the bugs would become widespread in the U.S. In the 1980s, an invasive mosquito species known as the Asian Tiger, an aggressive biter, arrived in a shipment of tires. It and another invasive species, the yellow fever mosquito, have colonized territory from the Mexican border to downtown Chicago. Both can transmit dengue, chikungunya and malaria.

Last fall, researchers from Texas A&M and the CDC looking for organisms carrying Chagas, including “kissing bugs,” reported that “over half of the new specimens found inside or near houses were infected” with the parasite. The bugs were found all over Texas often “in close proximity to human settings,” which suggested “the presence of an active peridomestic Chagas disease transmission cycle.”

There are more than five tropical diseases knocking on America’s door that concern public health experts.

# Leishmaniasis

Leishmaniasis is caused by a protozoa spread through phlebotomine sand fly bites. The most common cutaneous form of the disease causes skin lesions that can take months or even years to heal. Some forms can result in terrible facial deformities. Visceral leishmaniasis can cause a swollen spleen and liver, fever, weight loss, anemia, miscarriage and death.

Over 1,000 military personnel serving in Iraq have contracted cutaneous forms of the disease. A few have had visceral forms. Fortunately, both forms can be treated with anti-parasitic drugs. It also means that veterans can, and do, bring the parasite back into this country.

Cutaneous leishmaniasis has occurred in south Texas for years. In April of 2008, doctors in north Texas reported nine cases in people who had not traveled out of the region, meaning it originated in the state.

# Chagas

Chagas is a serious and growing problem in the U.S., although there are no specific statistics of infection rates, according to experts. “We do not have enough data to say what the magnitude is,” explained Caryn Bern, a Chagas expert at the CDC’s parasitic diseases branch. “There is a lot of speculation all over the map, anywhere from 100,000 to 1 million.” Bern estimates between 100,000 and 200,000 people living in the U.S. who have undiagnosed Chagas.

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# Dengue

Dengue, a mosquito-borne viral disease is sometimes called “break-bone fever” for the severe joint pain that accompanies it. The World Health Organization estimates that 2.5 billion people in 100 countries, including the U.S., are now at risk.

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# Malaria

By 1970, malaria, which had once plagued people from Manhattan’s Madison Avenue to rural Tennessee, was declared eradicated. But in 1999, two people in Suffolk County, New York were diagnosed with it. About 1,000 to 1,500 travelers every year enter the U.S. infected with malaria parasites, but the New York patients had not traveled anywhere. In 1999 and 2000, a few domestic cases showed up in Virginia and Maryland. In 2003, eight cases were found in Florida.

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# Chikungunya

Chikungunya, a viral illness transmitted by mosquitoes, causes headache, fever, nausea, vomiting, and muscle and joint pain. It was first isolated in 1953 and remained obscure until 2005 when a few cases were reported on islands in the Indian Ocean. Since then, it has sprinted across Asia and Africa.

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